Friendly Mûmak models gain the Harbinger of Evil (12") special rule.
The Scorpion’s Sting
Friendly models with the Poisoned Attacks (bow) special rule exchange it for Poisoned Attacks on all of their weapons.
Monstrous Rampage
Each Hero that is commanding a Mûmak can, once per game, declare a Heroic Combat for free whilst atop a Mûmak. When they do, the Mûmak will be affected as if they had been the one to declare the Heroic Combat, though they may not pivot before they Trample as part of a Heroic Combat.